Non-fibrous polymer solution of para-aramid with high relative viscosity

ABSTRACT

The invention relates to a non-fibrous polymer solution essentially consisting of 1 to 8 wt. % para-aramid, at least 50 mole % of the aromatic moieties thereof being unsubstituted, in a mixture of a) a polar amide solvent selected from N-methyl-2-pyrrolidone, N,N′-dimethyl-formamide, N,N′-dimethylacetamide, tetramethylurea, and mixtures thereof; b) between 0.7 mole of an alkali or alkaline earth metal chloride per mole amide groups of the para-aramid and 7.5 wt. % of the alkali or alkaline earth metal chloride, and c) water; and wherein at least 50 wt. % of the formed hydrochloric acid has been neutralized to obtain a solution having a dynamic viscosity which is at least a factor three smaller than the dynamic viscosity of the polymer solution without neutralization. The invention further pertains to a process making the same and para-aramid pulp-like fiber, paper and film made from said polymer solution.

CROSS REFERENCE

This Application is a national stage application of PCT/EP 2004/004695filed on May 4, 2004, the entire disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND

The present invention pertains to a non-fibrous polymer solution ofpara-aramid in a mixture of a polar amide solvent selected fromN-methyl-2-pyrrolidone, N,N′-dimethylformamide, N,N′-dimethylacetamide,tetramethylurea, and mixtures thereof, water, and an alkali or alkalineearth metal chloride, such as calcium chloride (CaCl₂) or lithiumchloride (LiCl). The invention further relates to (1) a method ofpreparing said solution, (2) a method of spinning the polymer solution,(3) a para-aramid pulp, (4) para-aramid paper and (5) para-aramid filmmade of said solution.

Para-oriented aromatic polyamides which are condensation polymers of apara-oriented aromatic diamine monomer and a para-oriented aromaticdicarboxylic acid halide monomer (hereinafter abbreviated to“para-aramids”) have hitherto been known to be useful in various fieldssuch as fiber, pulp and the like, because of their high strength, highelastic modulus and high heat resistance. Poly(para-phenyleneterephthalamide) (hereinafter abbreviated to “PPTA”) is one example of apara-aramid.

Hitherto, PPTA has been produced in polar amidesolvent/hexamethylphosphoramide (HMPA) or in polar amide solvent/saltsystems. Thus, PPTA is produced by carrying out a solutionpolymerization reaction in a polar amide solvent. The PPTA isprecipitated, neutralized, washed with water and dried, and onceisolated as a polymer. Then, the polymer is dissolved in a solvent andcan be made into a PPTA fiber by the process of wet spinning. In thisstep, concentrated sulfuric acid is used as the solvent for spinningdope, because PPTA is not readily soluble in organic solvents. Thisspinning dope usually shows an optical anisotropy.

Industrially, PPTA fiber is produced from a spinning dope usingconcentrated sulfuric acid as a solvent, considering the performances asa long fiber, particularly strength and stiffness.

According to the prior process, a pulp is produced by mechanicallycutting a PPTA fiber, dispersing the cut fiber in water and fibrillatingthe dispersed fiber by a mechanical shearing means such as beating orthe like, followed by filtration and drying. In such prior process, thesteps of polymerization, spinning, and pulp making are completelyindependent of one another. That is, the step of polymerization uses apolar amide solvent, the step of spinning uses concentrated sulfuricacid as solvent, and the step of pulp making uses water as a dispersingmedium. This is economically disadvantageous as an industrial process.

Therefore, it has been attempted to spin the polymer directly into pulp.In U.S. Pat. No. 4,959,453 and U.S. Pat. No. 5,021,123, afiber-containing non-pourable gel was prepared. After gelation, theproduct must be isolated by further dispersing the composition bydilution in a vigorously stirred precipitating medium comprising anon-solvent for the polymer. Spinning of this fibrous gel is verydifficult and fiber properties cannot be controlled. Further, it hasbeen disclosed that extrusion must be done under pressure and at hightemperature (i.e., 90° C.). Furthermore, it is required to useN-methyl-pyrrolidine in order to obtain pulp-like fibers, as wasdisclosed in Example A of U.S. Pat. No. 5,021,123.

In U.S. Pat. No. 3,673,143, particularly in Examples 8 and 9,para-aramid solutions were prepared. In Example 9, a chloro-substitutedpara-aramid was dissolved in N,N-dimethylacetamide (DMAc) without theaddition of an alkali or alkaline earth metal chloride. The latter isredundant, because these chloro-substituted para-aramids dissolve wellin DMAc. However, this is not the case when unsubstituted, orpara-aramids having more than 50 mole % of their aromatic moietiesunsubstituted, are used. It is known that these para-aramids areinsoluble in most solvents. In Example 8 of this reference, anunsubstituted para-aramid was dissolved in DMAc by adding large amountsof HMPA. HMPA, however, is highly carcinogenic and its use in industrialproduction of para-aramid polymers is prohibited.

WO 94/24211 discloses a solvent system wherein the toxic HMPA wasreplaced by substantial amounts of PVP. Although solutions with PVP aregood spinnable, their disadvantage is that the polymer is obtained as amixture of PPTA and PVP, thus the products (fibers, films, etc.) alsoare composed of mixed polymers. For many applications such mixedpolymers are unwanted.

In EP 572,002, pulp was prepared by producing para-aramid polymer inNMP/CaCl₂, spinning the fiber, and cutting and refining it into pulp.Although spinning takes place directly from PPTA in a mixture of NMP andcalcium chloride, this process has the disadvantage that fibers stillhave to be spun before cutting and refining. Furthermore, the molecularweight of the polymer solution and of the pulp obtained by such aprocess is limited, i.e., the polymer has a low relative viscosity, dueto the high dynamic viscosity of this solution.

SUMMARY

The first objective of the present invention is therefore to provide apara-aramid solution as a spinning dope, preferably exhibiting opticalanisotropy, and free from extra components such as pyridine, pyrimidine,N-methylpyrrolidine, or PVP, in order to obtain a spinning dope that candirectly be spun without applying high pressure and/or high spinningtemperature. Achieving this objective makes it possible to produce anaramid pulp-like fiber of pre-determined length. Further, para-aramidfilm and paper can be produced from the spinning dope.

When concentrated sulfuric acid is used, the steps for producing a fiberor a pulp-like fiber are quite complicated, and the apparatuses aretherefore quite expensive because corrosion by concentrated sulfuricacid must be avoided. Further, solvent systems that are toxic, such assystems comprising HMPA, are industrially impracticable.

Further, according to a process mentioned in U.S. Pat. No. 5,202,184, anaromatic diamine monomer and an aromatic dicarboxylic acid halidemonomer are subjected to a polycondensation reaction at an equimolarratio. An extrudate is formed from the polymer solution dope thatexhibits optical anisotropy in a stage prior to completion of thepolymerization. In such a process, the polymer solution dope is nothingmore than an intermediate taken out halfway through the polymerization.Thus, the polymer solution dope is in an unstable state and can beconverted to a high molecular weight substance or can form a gel. Thismakes it difficult to obtain a product of uniform quality and tocontinue the process. Thus, at the present stage, the process is notindustrially successful. Furthermore, no spinnable high-molecular weightsolution is obtained.

The second objective of the present invention is to overcome theabove-mentioned disadvantages by providing a process for producing astable polymer solution and a product of uniform quality according to anindustrially advantageous and simplified method, and to obtain pulp-likefibers with a high relative viscosity. In order to obtain pulp with highrelative viscosity in one step, a polymer solution with low dynamicviscosity is required to easily form fibrils.

These and other objectives have been achieved by a process for making anon-fibrous polymer solution, wherein an alkali or alkaline earth metalchloride is used as a replacement for HMPA. Surprisingly, it was foundthat the use of low amounts of these chlorides, i.e. 0.5 to 4.5 wt. %during the polymerization reaction, corresponding to at least 0.7 molechloride per mole amide group of the polymer and to a maximum of 7.5 wt.% of chloride in the final spinning solution (preferably from 0.9 moleto 7.0 wt. %), leads to complete dissolution of unsubstituted andpartially unsubstituted para-aramid in this solvent system. This isremarkable, because higher concentrations of chloride lower thesolubility of the para-aramid. At least partially neutralizing thesolution is necessary as non-neutralized solutions have increaseddynamic viscosity, making these solutions unsuitable for spinningpurpose for obtaining fibers and pulp having high relative viscosity. Itwas now found that the high dynamic viscosity of such solutions couldsubstantially be lowered when in addition to these chlorides, thehydrochloric acid formed during the polymerization is for at least 50wt. %, preferably for at least 75 wt. %, neutralized. Most preferably,the hydrochloric acid is completely neutralized. It was found that thedynamic viscosity could be lowered by a factor of at least 3, morepreferably by at least 5, most preferably by at least 10.

DETAILED DESCRIPTION

To this end the invention pertains to a method comprising the steps ofi) making a solution of aromatic diamine and aromatic dicarboxylic acidhalide monomers in a mixture of a polar amide solvent selected fromN-methyl-2-pyrrolidone, N,N′-dimethylformamide, N,N′-dimethylacetamide,tetramethylurea, and mixtures thereof, with 0.5 to 4.5 wt. % of analkali or alkaline earth metal chloride during polymerization,corresponding to at least 0.7 mole of an alkali or alkaline earth metalchloride per mole amide groups of the para-aramid and to a maximum of7.5 wt. % of the alkali or alkaline earth metal chloride in the finalpolymer solution, ii) polymerizing the monomers under the formation ofhydrochloric acid, and iii) neutralizing at least 50 wt. % of the formedhydrochloric acid with an inorganic base during or after thepolymerization of the monomers to para-aramid to obtain the finalpolymer solution.

According to another embodiment of the invention, a non-fibrous polymersolution of para-aramid in a mixture of NMP/CaCl₂, NMP/LiCl, orDMAc/LiCl is made, wherein the polymer solution has a relative viscosityη_(rel)>2.2.

Another aspect the invention relates to a non-fibrous polymer solutionessentially consisting of 1 to 8 wt. % para-aramid, at least 50 mole %of the aromatic moieties thereof being unsubstituted, in a mixture of a)a polar amide solvent selected from N-methyl-2-pyrrolidone,N,N′-dimethylformamide, N,N′-dimethylacetamide, tetramethylurea, andmixtures thereof; b) between 0.7 mole of an alkali or alkaline earthmetal chloride per mole amide groups of the para-aramid and 7.5 wt. % ofthe alkali or alkaline earth metal chloride, and c) water; and whereinat least 50 wt. % of the formed hydrochloric acid is neutralized toobtain a solution having a dynamic viscosity which is at least a factorof three smaller than the dynamic viscosity of the polymer solutionwithout neutralization.

The para-aramid polymer solution of the present invention exhibits a lowdynamic viscosity at a temperature up to about 60° C. in a shear raterange of 100-10,000 s⁻¹. For that reason the polymer solution accordingto the invention can be spun at a temperature below 60° C. Further, thepara-aramid dope of the present invention is free from extra componentssuch as pyridine, pyrimidine, N-methylpyrrolidine, or PVP. In addition,the para-aramid dope can be produced advantageously from the industrialpoint of view in that the production process can be simplified and theprocess is free from the problem of corrosion of apparatuses byconcentrated sulfuric acid as compared with the prior dopes usingconcentrated sulfuric acid as a solvent.

Further, according to the process of the present invention, the polymersolution can be directly spun, and the product can be made intopulp-like fibers without first making the yarn. Thus, the process ofproduction can be greatly simplified as compared with the priorproduction processes of para-aramid pulp-like fibers.

A para-aramid paper having a long breaking length can be produced fromthe para-aramid pulp-like fibers of the present invention. When used asa starting material of friction materials including automobile brake andthe like, the retention of filler is good. The pulp-like fibers aredirectly made from spinning the spin solution. Thus, the pulp-likefibers are made without first making yarns.

The invention therefore also relates to para-aramid pulp-like fibershaving preferably an ion content<250 ppm for fast migrating ions such asNa⁺ and Cl⁻ and a structural irregularity expressed as a difference inCSF (Canadian Standard Freeness) of never dried pulp and dried pulp ofat least 100, preferably of at least 150. This means that the fibrousbackbone of the pulp is highly kinky, which is not the case with thepulps that are known in the prior art. Preferably the para-aramidpulp-like fibers have a relative viscosity (η_(rel)) larger than 3.7. Inthis respect the term “kinky” means that the fiber backbone extendsrandomly in any direction.

In another embodiment, the invention also pertains to para-aramid filmobtainable from the polymer solution of the invention.

The present invention will now be explained in more detail below.

As used in the present invention, the term “para-aramid” means asubstance obtained by a polycondensation of a para-oriented aromaticdiamine monomer and a para-oriented aromatic dicarboxylic acid halidemonomer of which recurring units have amide bonds located substantiallyin the para-oriented or nearly para-oriented opposite positions ofaromatic ring, namely in such coaxially or in-parallel arrangedpositions as those of para phenylene, 4,4′-biphenylene, 1,5-naphthaleneand 2,6-naphthalene.

Concrete examples of said para-aramid include the aramids of whichstructures have a poly-para-oriented form or a form close thereto, suchas poly(paraphenylene terephthalamide), poly(4,4′-benzanilideterephthalamide), poly(paraphenylene-4,4′-biphenylenedicarboxylic acidamide) and poly-(paraphenylene-2,6-naphthalenedicarboxylic acid amide).Among these para-aramids, poly(paraphenylene terephthalamide) is mostrepresentative.

As used in the present invention, the term “pulp-like fibers” meanssmall fibers with a length less than 50 mm that are stronglyfibrillated. According to this invention, paper is a form of pulp-likefibers that can be directly obtained or be made from pulp-like fibers,optionally in combination with other types of fiber. The term “film”means a layer of non-fibrous material.

This stable spin dope has a para-aramid concentration of 1-8 wt. % and amoderate to high degree of polymerization to allow high relativeviscosity (η_(rel)>2.2). Depending on the polymer concentration the dopeexhibits an anisotropic (polymer concentration>1.5%) or an isotropicbehavior. Preferably, the dynamic viscosity η_(dyn) is smaller than 10Pa·1, more preferably smaller than 5 Pa·s at a shear rate of 1000 s⁻¹.

At least partial neutralization takes place during or preferably afterpolymerizing the monomers forming the para-aramid. The neutralizationagent is not present in the solution of monomers before polymerizationhas commenced. Neutralization reduces dynamic viscosity by a factor ofat least 3, preferably by a factor of at least 5, more preferably of atleast 10. The neutralized polymer solution can be used for direct pulpspinning using a nozzle, contacting the polymer stream by pressurizedair in a zone with lower pressure where the polymer stream is brokeninto droplets by expansion of the air. The droplets are attenuated into(pulp-like) fibers.

Coagulation of the fibers or pulp-like fibers takes place using asuitable coagulant such as water or water/NMP/CaCl₂. Instead of CaCl₂other chlorides such as LiCl may also be used. By adjusting the polymerflow/air flow ratio, the length and the fibrillation degree of the pulpcan be changed. At high ratios long, less fibrillated pulp is obtained,while at low ratios a short, highly fibrillated pulp is obtained.

The pulp-like fibers of the present invention are useful as a startingmaterial for para-aramid paper, friction materials including automobilebrakes, various gaskets, E-papers (for instance for electronic purposes,as it contains very low amounts of ions compared to para-aramid pulpmade from sulfuric acid solutions), and the like. The water jet can beomitted and the pulp/fibers are then laid down in the form of a sheet ornon-woven, after which coagulation takes place.

Examples of the para-oriented aromatic diamine usable in the presentinvention include para-phenylenediamine, 4,4′-diaminobiphenyl,2,6-naphthalenediamine, 1,5-naphthalenediamine, and4,4′-diaminobenzanilide. A maximum of 50 mole % of substituted aromaticdiamines may be used, such as 2-methyl-para-phenylenediamine and2-chloro-para-phenylenediamine.

Examples of para-oriented aromatic dicarboxylic acid halide usable inthe present invention include terephthaloyl dichloride, 4,4′-benzoyldichloride, 2,6-naphthalenedicarboxylic acid dichloride, and1,5-naphthalenedicarboxylic acid dichloride. A maximum of 50 mole % ofsubstituted aromatic dicarboxylic acid halide may be used, such as2-chloroterephthaloyl dichloride, 2,5-dichloroterephthaloyl dichloride,2-methylterephthaloyl dichloride.

The total of substituted aromatic diamine and aromatic dicarboxylic acidhalide monomers should be less than 50%. Preferably, at least 70% of thearomatic moieties of the polymer are unsubstituted.

In the present invention 0.950-1.050 mole, preferably 0.980-1.030, morepreferably 0.995-1.010 mole of para-oriented aromatic diamine is usedper 1 mole of para-oriented aromatic carboxylic acid halide in a polaramide solvent in which 0.5-4.5 wt. % of alkali metal chloride oralkaline earth metal chloride is dissolved, making the concentration ofpara-aramid obtained thereof 1-8 wt. %, preferably 1-6 wt. %, morepreferably 3-5.5 wt. %. In the present invention the polymerizationtemperature of para-aramid is −20° C. to 70° C., preferably 0° C. to 30°C., and more preferably 5° C. to 25° C. In this temperature range, thedynamic viscosity is within the required range and the pulp-like fiberproduced thereof by spinning can have sufficient degree ofcrystallization and degree of crystal orientation.

Examples of the chlorides of alkali metal or alkaline earth metal usablein the present invention include lithium chloride and calcium chloride.Specific examples of the polar amide solvent usable in the presentinvention include N-methyl-2-pyrrolidone, N,N′-dimethylformamide,N,N-dimethylacetamide, and tetramethylurea.

The mixture according to this invention also contains minor amounts ofwater, at least due to the neutralization reaction. Usually, the watercontent is less than 5 wt. %, preferably less than 1 wt. %.

An essential feature of the present invention is that the polymerizationreaction may be first enhanced and thereafter stopped by at leastpartially neutralizing the polymer solution or the solution forming thepolymer by adding an inorganic base, preferably calcium oxide or lithiumoxide. In this respect the terms “calcium oxide” and “lithium oxide”comprise calcium hydroxide and lithium hydroxide, respectively. Thisneutralization effects the removal of hydrogen chloride, which is formedduring the polymerization reaction. Neutralization results in a drop ofthe dynamic viscosity with a factor of at least 3 (with regard to anon-neutralized corresponding solution). After neutralization, thechlorides are present in an amount of at least 0.7 moles, morepreferably in an amount of at least 0.9 moles, per mole of the amidegroup formed in the polycondensation reaction. The total amount ofchloride may originate from CaCl₂, which is used in the solvent and fromCaO or Ca(OH)₂, which is used as a neutralizing agent (base) up to amaximum of 7.5 wt. %, preferably 7.0 wt. %. If the calcium chloridecontent is too high or too low, the dynamic viscosity of the solution israised too much to be suitable as a spin solution.

The liquid para-aramid polymerization solution can be supplied with theaid of a pressure vessel to a spinning pump to feed a nozzle for jetspinning of 100-1000 μm to pulp-like fibers. The liquid para-aramidsolution is spun through a spinning nozzle into a zone of lowerpressure. For air jet spinning more than 1 bar, preferably 4-6 bar isseparately applied through a ring-shaped channel to the same zone whereexpansion of air occurs. Under the influence of the expanding air flowthe liquid spinning solution is divided into small droplets and at thesame time or subsequently oriented by drawing. Then the pulp-like fibersare coagulated in the same zone by applying a coagulant jet and theformed pulp is collected on a filter, or directly processed to paper.Alternatively, the fibers are laid down on a plate to directly formpaper and thereafter coagulated. The coagulant is selected from water,mixtures of water, NMP, and CaCl₂, and any other suitable coagulant.

The present invention will now be explained by way of the followingnon-limitative examples.

The methods of test and evaluation and criteria of judgment employed inthe examples and comparative examples were as follows.

Test Methods

Relative Viscosity

The sample was dissolved in sulfuric acid (96%) at room temperature at aconcentration of 0.25% (m/v). The flow time of the sample solution insulfuric acid was measured at 25° C. in an Ubbelohde viscometer. Underidentical conditions the flow time of the solvent is measured as well.The viscosity ratio is then calculated as the ratio between the twoobserved flow times.

Dynamic Viscosity

The dynamic viscosity is measured using capillary rheometry at roomtemperature. By making use of the Powerlaw coefficient and theRabinowitsch correction, the real wall shear rate and the viscosity havebeen calculated.

Fiber Length Measurement

Fiber length measurement was done using a Kajaani FS200. As length the‘Weight weighted length’ (WL) was used as a measure for the pulp length.

Specific Surface Area (SSA) Determination

Specific surface area (m²/g) was determined using adsorption of nitrogenby the BET specific surface area method, using a Gemini 2375manufactured by Micromeretics. The wet pulp samples were dried at 120°C. overnight, followed by flushing with nitrogen for at least 1 hour at200° C.

Evaluation of Optical Anisotropy (Liquid Crystal State)

Optical anisotropy is examined under a polarization microscope (brightimage) and/or seen as opalescence during stirring.

Redispersability Test

3 g (dry weight) of never dried pulp is dispersed in 1 l of water during1000 beats in a Lorentz and Wettre desintegrator. A well-opened pulp isobtained. The Canadian Standard Freeness (CSF) value is measured andcorrected for slight differences in weight of the pulp (Tappi 227).

3 g (dry weight) of never dried pulp is dispersed in 1 l water during1000 beats in a Lorentz and Wettre desintegrator. A handsheet is madefrom this pulp, which is dried in a sheet dryer (Labtech) during 1 hourat 120° C. After drying the handsheets are torn by hand into smallpieces (˜3×3 cm) and put into 1 l of water. The pulp is redispersed inan L&W mixer during 1000 beats and the CSF value is measured andcorrected for slight differences in weight of the pulp.

EXAMPLE 1

Polymerization of para-phenyleneterephthalamide was carried out using a160 l Drais reactor. After sufficiently drying the reactor, 64 l ofNMP/CaCl₂ (N-methylpyrrolidone/calcium chloride) with a CaCl₂concentration of 2.5 wt. % were added to the reactor. Subsequently, 1487g of para-phenylenediamine (PPD) were added and dissolved at roomtemperature. Thereafter the PPD solution was cooled to 10° C. and 2772 gof terephthaloyl dichloride (TDC) were added. After addition of the TDC,the polymerization reaction was continued for 45 min. Then, the polymersolution was neutralized with a calcium oxide/NMP-slurry (776 g of CaOin NMP). After addition of the CaO-slurry, the polymer solution wasstirred for at least another 15 min. This neutralization was carried outto remove the hydrochloric acid (HCl), which is formed duringpolymerization. A gel-like polymer solution was obtained with a PPTAcontent of 4.5 wt. % and having a relative viscosity of 3.8 (in 0.25%H₂SO₄). The obtained solution exhibited optical anisotropy and wasstable for more than one month.

EXAMPLES 2, 3, AND 4

These examples were carried out as in Example 1 with the molar ratios ofPPD and TDC as given in Table 1. These examples show that by adjustingthe monomer ratio, the degree of polymerization is changed. Reactiontime was as stated in Table 1.

The solution of Example 2 was supplied (11 kg/h) with the aid of apressure vessel to a spinning pump to feed the spinning nozzle of 350μm. The spinning temperature was ambient. The PPTA was spun through thenozzle into a zone of lower pressure. An air jet of 7 bar was separatelyapplied through a ring-shaped channel to the same zone where expansionof the air occurred. Thereafter, the pulp was coagulated in the samezone by means of applying a coagulant jet (1110 kg/h) and the formedpulp was collected on a filter. Water was used as the coagulant. Theresulting pulp (relative viscosity 2.4) had a length of 1.2 mm, an SSAof 6.9 m²/g and a CSF of 175.

EXAMPLE 5

This Example was carried out as Example 1 with a molar ratio of PPD andTDC of 1.000. In order to obtain a solution with a relative viscosity of2.4 a small amount (30 ml) of H₂O was added to the NMP solution.

EXAMPLE 6

The polymer solution of Example 1 was diluted with NMP to a polymerconcentration of 3.6 wt. %. The resulting solution was gel-like andshowed optical anisotropy. This polymerization solution was supplied (8kg/h) with the aid of a pressure vessel to a spinning pump to feed thespinning nozzle of 350 μm. The spinning temperature was ambient. ThePPTA was spun through the nozzle into a zone of lower pressure. An airjet of 7 bar was separately applied through a ring-shaped channel to thesame zone where expansion of the air occurred. Thereafter, the pulp wascoagulated in the same zone by means of applying a coagulant jet (1500kg/h) and the formed pulp was collected on a filter. Water was used asthe coagulant. The resulting pulp (relative viscosity 3.8) had a lengthof 1.2 mm, an SSA of 1.9 m²/g and a CSF of 480. After preparing a papersheet of this material and drying, the sheet was torn in pieces and theCSF was strongly increased to 666.

EXAMPLE 7

This time the solution of Example 1 was diluted with NMP to a polymerconcentration of 1 wt. %. The 1 wt. %-polymer solution is now clearlyisotropic of character.

EXAMPLE 8

Polymerization of para-phenyleneterephthalamide was carried out using a160 l Drais reactor. After sufficiently drying the reactor, 64 l ofNMP/CaCl₂ with a CaCl₂ concentration of 3.3 wt. % were added to thereactor. Subsequently, 2050 g of PPD were added and dissolved at roomtemperature. Thereafter, the PPD solution was cooled to 10° C. and 3792g of TDC were added. After addition of the TDC, the polymerizationreaction was continued for 45 min. Then, the polymer solution wasneutralized with a calcium oxide/NMP-slurry (1047 g of CaO in NMP).After addition of the CaO-slurry, the polymer solution was stirred for30 min. This neutralization was carried out to remove the HCl, which isformed during polymerization. A gel-like polymer solution was obtainedwith a PPTA content of 5.9 wt. % and having a relative viscosity of 2.6(in 0.25% H₂SO₄).

EXAMPLE 9

Polymerization was carried out as in Example 1. The dynamic viscosity ofthe polymer solution was found to be 2 Pa·s at 1000 s⁻¹.

EXAMPLE A (COMPARATIVE)

This example shows what happens when no neutralization is carried out.Polymerization was carried out as in Example 9 with the exception thatno CaO-slurry was added. The polymerization resulted in a crumbledreaction product with a dynamic viscosity 30 Pa·s at 1000 s⁻¹.

EXAMPLE B (COMPARATIVE)

This example illustrates what happens when no neutralization is carriedout. Polymerization was carried out as in Example 8 with the exceptionthat no CaO-slurry was added. The polymerization resulted in a crumbledreaction product.

EXAMPLE C (COMPARATIVE)

The CSF of a wet highly-fibrillated prior art standard TWARON® pulpcharacterized by a SSA of 13.5 m²/g and a WL of 1.4 equalled 130. Afterpreparing a paper sheet of this material and drying, the sheet was tornin pieces and the CSF only slightly increased to 165. TABLE 1 ExampleExample Example Example Example Example Example Example Example ExampleExample 1 2 3 4 5 6 7 8 9 A B CaCl₂/amide 1.08 1.06 1.19 1.07 1.07 1.091.05 1.01 1.09 1.04 1.06 (mole/mole) at end PPD/TDC 1.007 1.010 1.0040.994 1.000 1.007 1.007 1.015 1.007 1.007 1.016 (mole/mole)Polymerization 45 55 37 47 5 45 45 45 45 45 45 time (min) η_(rel) 3.82.4 4.3 5.8 2.4 3.8 3.8 2.6 3.4 2.6 2.4 Polymer conc. 4.5 4.5 4.8 4.44.4 4.5 4.5 5.9 4.4 4.6 5.9 (wt. %) Neutralization yes yes yes Yes yesyes yes yes yes no no Diluted with — — — — — 3.6 wt. % 1 wt. % — — — —NMP

1. A non-fibrous polymer solution comprising 1 to 8 wt. % para-aramid,wherein at least 50 mole % of aromatic moieties of the para-aramid areunsubstituted, in a mixture of a) a polar amide solvent selected from agroup consisting of N-methyl-2-pyrrolidone, N,N′-dimethylformamide,N,N′-dimethylacetamide, tetramethylurea, and mixtures thereof; b) from0.7 mole of an alkali or an alkaline earth metal chloride per mole amidegroups of the para-aramid to 7.5 wt. % of the alkali or the alkalineearth metal chloride in the polymer solution; and c) water; and whereinat least 50 wt. % of formed hydrochloric acid is neutralized to obtain asolution having a dynamic viscosity which is at least a factor of threesmaller than a dynamic viscosity of the polymer solution withoutneutralization.
 2. The polymer solution of claim 1, wherein the solutionis an anisotropic solution of para-aramid in a mixture ofN-methyl-2-pyrrolidone (NMP) and calcium chloride (CaCl₂), or in amixture of dimethylacetamide (DMAc) and lithium chloride (LiCl).
 3. Thepolymer solution of claim 1 having a dynamic viscosity η_(dyn)<10 Pa·sat a shear rate of 1000 s⁻¹.
 4. The polymer solution of claim 1 whereinthe solution comprises 1 to 6 wt. % of para-aramid.
 5. The polymersolution of claim 1, wherein the para-aramid is PPTA.
 6. A process formaking the polymer solution of claim 1, comprising the steps of i)making a solution of aromatic diamine and aromatic dicarboxylic acidhalide monomers in a mixture of a) a polar amide solvent selected fromthe group consisting of N-methyl-2-pyrrolidone, N,N′-dimethylform-amide,N,N′-dimethylacetamide, tetramethylurea, and mixtures thereof, and b)0.5 to 4.5 wt. % of an alkali or an alkaline earth metal chloride duringpolymerization, corresponding to from at least 0.7 mole of the alkali orthe alkaline earth metal chloride per mole amide groups of thepara-aramid to a maximum of 7.5 wt. % of the alkali or the alkalineearth metal chloride in a final polymer solution, ii) polymerizing themonomers to para-aramid under the formation of hydrochloric acid, andiii) neutralizing at least 50 wt. % of the formed hydrochloric acid withan inorganic or a strong organic base during or after the polymerizationof the monomers to para aramid to obtain the final polymer solution. 7.The process according to claim 6, wherein the formed hydrochloric acidis neutralized with calcium oxide, calcium hydroxide, lithium oxide orlithium hydroxide.
 8. A method of spinning the polymer solution of claim1, wherein the solution is spun at a temperature below 60° C.
 9. Apara-aramid pulp-like fiber having a structural irregularity expressedas a difference in Canadian Standard Freeness (CSF) of never dried pulpand dried pulp of at least
 100. 10. The para-aramid pulp-like fiber ofclaim 9, wherein the difference in CSF of never dried pulp and driedpulp is at least
 150. 11. The para-aramid pulp-like fiber of claim 9,wherein the structural irregularity is contained in a kinky structure ofthe fibrous backbone of the pulp.
 12. The para-aramid pulp-like fiber ofclaim 9, wherein relative viscosity (η_(rel)) of the para-aramidpulp-like fiber is larger than 3.7.
 13. A para-aramid paper formed fromthe polymer solution of claim
 1. 14. A para-aramid film formed from thepolymer solution of claim 1.